Difference Between Digestion and Absorption

The key difference between digestion and absorption is that digestion is the process of breaking foods into their building blocks by mechanical and chemical processes while absorption is the assimilation of nutrients into the bloodstream.

Food that animals eat goes through four main processes known as ingestion, digestion, absorption, and defecation. Ingestion happens first which is then followed by digestion, and finally, the absorption of nutrients in digested food takes place to generate energy. Both digestion and absorption processes take place in the alimentary tract of an animal. These two processes are completely different processes. However, it is impossible for absorption to take place without digestion. Hence, absorption always follows digestion. Accordingly, digestion facilitates the absorption of necessary nutrients into our blood.

CONTENTS

1. Overview and Key Difference
2. What is Digestion
3. What is Absorption
4. Similarities Between Digestion and Absorption
5. Side by Side Comparison – Digestion vs Absorption in Tabular Form
6. Summary

What is Digestion?

Generally, digestion is the breaking down of food inside the digestive tract. This process constitutes a series of processes. Likewise, there are two main types of digestion namely mechanical digestion and chemical digestion. In digestion, simplification of large molecules into small monomers takes place. Hence, it is a process of catabolism. However, there are mainly two forms of digestive systems; primitive organisms have external digestion, while more evolved advanced animals have internal digestive systems.

In advanced animals, digestion starts in the mouth and continues through to stomach and concludes at jejunum. While food passes through the oesophagus, the peristaltic movements help to break down it into smaller particles. Inside the stomach, the chemical digestion becomes predominant with the secretion of digestive enzymes and acids with optimum temperature. Protein digestion starts in the stomach and ends up in the small intestine after converting proteins to amino acids. Lipid digestion starts and ends in the small intestine, which converts lipids into glycerol and fatty acids. Mouth starts carbohydrate digestion, and it concludes at the small intestine after forming simple sugars. After all the digestive processes, the nutrients in food are ready for absorption into the bloodstream.

What is Absorption?

Absorption is transferring the digested molecules across the gastrointestinal tract into the bloodstream. Absorption starts in the stomach, continues through the small intestine, and concludes at the large intestine. There are four main mechanisms responsible for absorption such as active transport, passive diffusion, endocytosis, and facilitative diffusion.

Simple columnar epithelial tissue covers the interior wall of the intestine with folds called plicae circulars those increase the area of absorption. Additionally, microscopic finger-like processes called villi and microvilli are present in the folds with each having a network of capillaries. These capillaries transfer nutrients from food into the bloodstream. Jejunum and ileum absorb most of the nutrients while large intestine does the majority of the water absorption. Finally, after absorption at the large intestine, the undigested and unabsorbed portion is ready for defecation.

What are the Similarities Between Digestion and Absorption?

• Digestion and absorption are two processes of the digestive system.
• Absorption follows digestion.
• These two processes are extremely important for the survival of organisms.
• Also, both require energy to carry out.

What is the Difference Between Digestion and Absorption?

Digestion and absorption are two of the processes that occur in our digestive system. Ingestion is the first process, then digestion and the absorption follows digestion. Digestion is the process that breaks food into small pieces and then into molecules. Absorption is the process of absorbing nutrients in the form of molecules into the blood. Therefore, this is the key difference between digestion and absorption.

Digestion starts in the mouth while absorption starts in the stomach. Moreover, digestion occurs from mouth to intestine while absorption mostly occurs from the stomach to intestine. So, this is another difference between digestion and absorption.

The below infographic illustrates more details on the difference between digestion and absorption.

Summary – Digestion vs Absorption

Once we ingest foods, they undergo digestion and absorption. Hence, digestion and absorption are two processes that occur in the animal digestive tract. Here, the digestion takes place first and then the absorption. Digestion is the process of breaking down the food into small pieces by mechanically and then into molecules by chemically. On the other hand, absorption is the process of absorbing nutrients into the bloodstream. Thus, it is the key difference between digestion and absorption. Chemical digestion mainly occurs due to enzymes while absorption does not need enzymes.

Furthermore, digestion utilizes energy while some of the absorption mechanisms do not need energy. Digestion mostly occurs in the stomach while absorption mostly occurs in the intestine. Thus, this is the summary of the difference between digestion and absorption.

Reference:

1.“Digestion.” Wikipedia, Wikimedia Foundation, 18 Dec. 2018. Available here 

Image Courtesy:

1.”2405 Digestive Process”By OpenStax College – Anatomy & Physiology, Connexions Web site. Jun 19, 2013., (CC BY 3.0) via Commons Wikimedia  
2.”Figure 34 01 11f”By CNX OpenStax  (CC BY 4.0) via Commons Wikimedia